4 Replies Latest reply on Sep 3, 2019 3:45 PM by shge_4395051

    AMUX Functionality

    shge_4395051

      Hello

      I've been using the CY8CKIT-147 PSoC 4100PS Prototyping Kit and have been fighting an issue with the AMUX.  I have a 4x1 AMUX which switches in 4 possible feedback resistor values.  The voltages at the input are different from the output of the AMUX.  If I remove the AMUX and hardwire one of the resistors in place, the design works fine.  I have attached the design. Any advice would be appreciated.

      thanks

      Shawn

        • 1. Re: AMUX Functionality
          VasanthR_91

          Hello Shawn,

           

          How much variation are you seeing at opamp input and amux input pins ? Are you getting the outputs near the expected range ? Could you please let me know the output observed at your end ?,

          Best Regards

          Vasanth

          • 2. Re: AMUX Functionality
            shge_4395051

            Hello Vasanth

             

            If I fix my input to the OpAmp at 100mV and select channel 3 of the AMux (gain = 2), I receive 20mV at the output of the OpAmp.

             

            If I remove the Amux and hardwire in a 1K ohm resistor, I receive the correct value of 200mV.  So I suspect the AMux.

             

            Shawn Gerber

            Manufacturing Engineer Manager

            Wagner Electronic Products Inc.

            326 Pine Grove Road

            Rogue River, OR 97537

            Office: (541) 582-0541 x238

            http://www.WagnerMeters.com/<http://www.wagnermeters.com/>

            • 3. Re: AMUX Functionality
              NoriakiT_91

              This is caused by the routing resistance inside the chip.

              For example, the resistance between the Pin_1K pin (P2[4]) and the Pin_14K pin (P3[3]) is estimated as 2150homs.

              GS004528.png

              This resistance value cannot be ignored as the feedback resistor network.

              It is recommended not to flow much current through the AMXU.

              GS004529.png

              Please adjust the resistance value of the output voltage divider.

              • 4. Re: AMUX Functionality
                shge_4395051

                Thanks for your reply.  I don’t thing the issues I’m having are a result of internal resistance.  The circuit is acting like an attenuator.  I input 100mV and receive 20mV at the output with the 1K feedback resistor switched in.

                 

                Also, I’m not running a lot of current through the AMux.  I feel like the Amux circuits are not performing as they should.  Is the 4100PS a new device?  Should I try other devices?

                 

                thanks